ROLE OF PROTEIN-KINASE-C ON THE ACUTE DESENSITIZATION OF RENAL CORTICAL ADENYLATE-CYCLASE TO PARATHYROID-HORMONE

The mechanisms of adenylate cyclase desensitization to parathyroid hor mone are still unclear. Current evidence suggest that the signal gener ated after PTH binding to receptors results in activation of adenylate cyclase and stimulation of phospholipase C with subsequent activation of protein kinase C. Recent studies have suggested a role of protein kinase C on the regulation of the PTH-dependent receptor-adenylate cyc lase system in cultured cells. Therefore, the present studies were con ducted to examine the role of protein kinase C on the desensitization of canine renal cortical adenylate cyclase after an acute exposure in vivo to PTH. A group of normal dogs were treated with a single intrave nous injection of 1 mu g/k of syn bPTH (1-34) or Me bPTH (3-34). Ten m inutes later, animals were subjected to bilateral nephrectomy and the kidney cortex processed for preparations of basolateral membranes for determinations of adenylate cyclase activity, as well as membrane and cytosolic fractions for analysis of protein kinase C activity. Animals not treated with PTH were used as controls. PTH administration in viv o resulted in a 46.9 +/- 9.3% decrease in maximal adenylate cyclase ac tivity in vitro in response to syn bPTH (1-34) (P < 0.001). Likewise, PTH binding as measured with I-125-Nle(8'18),Tyr(34)-bPTH (1-34)NH2 sh owed a 40 +/- 3% decrease. This alterations were associated with a mar ked translocation of protein kinase C from the cytosol to the membrane . Thus, protein kinase C activity in membrane fractions increased from 160.6 +/- 44.8 pmol Pi/min in controls to 500.4 +/- 123 in PTH treate d dogs (P < 0.03). Conversely, cytosolic activity decreased from 492.3 +/- 100 pmol Pi/min in controls to 260 +/- 127 in PTH treated animals . Treatment of the animals with Me bPTH (3-34) also resulted in transl ocation of protein kinase activity of similar magnitude. These data in dicate that acute homologous desensitization of the receptor-adenylate system after PTH administration in vivo occurs in association with tr anslocation of protein kinase C activity, suggesting a role of this sy stem in the mechanism of desensitization of adenylate cyclase to the h ormone.